Process for the preparation of pure manganese



June 17, 1969 c p sc uo ET AL 3,450,524 PROCESS FOR THE PREPARATION OF PURE MANGANESE Filed Oct. 31, 1966 INVENTORS. Claude Pascaud BY Louis Graff THEIR ATTORNEYS United States Patent Int. Cl. "C221! 3718; C22b 47/00 U.S. Cl. 75-65 Claims By the utilization of electrolytic refining processes, it is possible to prepare from an impure metal, such as chromium, titanium, zirconium, and vanadium, a metal of high purity. The initial alloy used as a soluble anode is connected to the positive terminal of a direct current generator. 'l he electrolytic bath is often .formed from a mixture of alkaline or alkaline-earth salts together with a halide of the metal to lbe refined whereby the pure metal is deposited on the apparatus cathode. The operation is carried out at a temperature at which the salt bath is molten, and under an inert atmosphere. However, it is not possible in this manner to eliminate all of the impurities present in the impure metal as an alloy element or as a definite compound, because certain metals and compounds are deposited on the cathode together with the desired metal and certain compounds are not eliminated during the electrolysis.

Until now, the attempts for obtaining high purity manganese by electrolysis in an igneous medium had led to delicate and costly conditions of preparation.

Contrary to the general belief, we have discovered that it is possible to obtain highly pure manganese trom very impure alloys by electrolysis in a bath of molten salts. In particular the inventive process comprises the electrolytic refining of a soluble anode formed of manganese alloy in a molten bath containing manganese chloride and at least one element from the group consisting of alkaline and alkaline-earth chlorides, removing the cathode from the bath at the end of the operation, and extracting the pure manganese from the salt and metal magma collected on the cathode.

Diverse manganese alloys may be utilized; however, it is particularly advantageous to use terromanganese. It is possible to utilize a previously refined rferroma-nganese and, also, the ferromanganese carbides wherein practically all the manganese is combined as M-n C.

Generally, when the electrolysis is carried out at a temperature ranging between 700-800" C., the cathode is removed at the end of the electrolytic operation and cooled under an inert atmosphere to prevent the reaction between the pure manganese deposited and the air components. However, the present process eliminates the need tor an inert atmosphere :by carrying out the electrolysis at a temperature not above 600 C., whereby the composition :salt bath gives an adequate melting temperature, and permits the direct removal and cooling of the cathode in free air. At such a temperature the manganese does not noticeably react with the air components. Thus, there is no need for a special apparatus tor keeping the atmosphere inert while the cathode is removed and cooled.

The electrolytic process is preferably carried out with the baths having a melting temperature below 530 C. so that the difference between the working .temperature which advantageously does not exceed 600 C.-and the melting temperature of the bath should be sufiicient to allow a good dripping of the cathode when removed from the electrolytic cell. There are various salt bath compositions that fulfill the melting temperature condition. For instance, the baths of the following general composition have a melting temperature below 600 C.:

Percent MnCl 1-20 CaCl 40-70 KCl 0-10 NaCl Remainder Percent MnOl 1-20 NaCl+LiCl 10-59 CaC1 +l3aCl 40-70 KCl 0-10 A101 0-20 Not absolutely necessary that both salts be present.

An example of baths with melting points of approximately 520 C. are:

By replacing one or more of the compounds selected [from the group consisting of CaCl NaCl, and KCl with one or more compounds selected from the group consisting of 'BaCl A101 and LiOl, it is possible to form other baths with similar melting points. For economic reasons MnC1 NaCl, and CaC1 are preferred.

The manganese collected on the cathode may be separated by melting the solidified salts when the cathode mass is removed from the bath. In particular, the pure manganese deposited on the cathode is separated by remelting the salt and extracted metal magma, where the remelting comprises two phases: the cathode is placed into an inert atmosphere furnace first heated slightly above the melting point of the salt bath, so as 'to melt the salts of the magma and not the manganese, a portion of this molten bath is eventually extracted, then the temperature is raised above the melting point of the manganese (for instance to 1290 C.) so as to melt the manganese which is surmounted with a protective layer of molten salts, and said manganese is cast into an ingotm-old under this protective layer.

The iollowing example is a complete illustration of the invention process. The particular apparatus utilized is represented in the drawing. It comprises:

A cylindr-ic cell 1 of mild steel containing the electrolytic bath 19. Said cell is enclosed in an external casing 2 of refractory insulating material. The electrolytic bath is heated by electrical resistances 3 or burners 4.

An anodic set 5 comprising a number of cylindric baskets 6, made of perforated sheet, provided with a perforated bottom, and containing the impure metal to be refined. Such an arrangement, is preferable to one annular basket, because it facilitates the progressive exchange of baskets when the mass of anodic metal is exhausted of manganese and also because it .aids the electric bath to circulate more readily through the charge. These baskets are mechanically and electrically connected to .a flange 7, and electrically insulated from the other parts of the apparatus, and connected to the positive terminal of the direct current generator. A lid 8 resting on flange 7 with interposition of an elastomer gasket 10 ensuring a seal and electric insulation. A quickly re- 3 movable clamping device 9 cleats the lid on flange 7 integral to the cell.

A cathode 18 on which the refined manganese is deposited is connected electrically to the negative terminal of the direct current generator and mechanically to a body 12 electrically insulated from the lid. A quickly removable junction 13 insures both mechanical joinder and excellent electrical contact. At its lower extremity, cathode 18 has a disc 17 to gather the manganese crystals that would accidently be separated from the cathodic deposit.

The cathode may be of various shapes, for example, it may be a cylindric solid, hollow rod, ribbed section, or

multiple rods electrically and mechanically connected together.

Cooling circuits 14 are provided to maintain the elastomer gaskets at a temperature below their decomposition temperature, and the external parts at a temperature not dangerous for handling. Other devices may be annexed to the apparatus, such as sighting scuttles, temperature taps at various points, safety valves, and measuring and regulation instruments.

A removable intermediary bottom 15 formed of a perforated sheet doubled with a close meshed grid of 0.5 to 1 mm. and having a few-centimeter-high edge is provided to collect the crystals that are separated from the cathode, as well as the sludges which are normally formed after a long working-time of the cell and which result, among other causes, from the mechanical breaking of the anodic charge. Said bottom may be removed, after the lid and the baskets have been taken ofi, by means of rods 16.

The electrolytic current utilized has an intensity of 1-100 a./dm. at 0.01 to 3 volts.

A number of variations of the apparatus are possible. With regard to heating the cell, insofar as the electrolytic direct current is insuflicient to keep the bath at its working temperature, external electric resistances or liquid or solid fuel burners may be utilized; it is also possible to heat the bath by means of a number of auxiliary metallic electrodes extending into the bath, utilizing a low alternating voltage current, while taking care that both electrolytic and auxiliary heating electric circuits have no common points. If the latter way of heating is adopted, the cell may be formed from a shell of thin sheet, highly insulated outside, and coated inside with a casing of ceramic material formed from alumina or silico-alumina compounds or any other material resistent to the action of the electrolytic bath.

To obtain a good yield from the direct current generator, it is preferable to electrically set a number of cells in series, the anode of the first one being connected to the positive terminal of the generator and its cathode to the anode of the second, the cathode of the second to the anode of the third, and so on to the last cell, the cathode of which is connected to the negative terminal of the generator.

EXAMPLE Into the anodic baskets were placed bits of ferromanganese of the following composition:

For 24 hours, a direct current was applied under 1.3 v.

4 The intensity increased progressively from 200 a. to 250 a. The whole amount of electricity utilized was 5,350 amperes-hours. The cathode deposit, weighing 7,130 g. after dripping, was removed without any particular precaution. Without waiting for its complete cooling, it was introduced into the alumina crucible of an induction furnace in which the atmosphere was argon. The temperature being brought to 650 C., the salt retained by the manganese crystals melted and collected at the bottom of the crucible. The major part of said salt was drawn 01? and recovered to be later recycled in the electrolytic cell. The temperature of the furnace was then brought to 1,290 C. (melting point of Mn 1,260 C.). The liquid manganese surmounted with a liquid layer was cast in an ingot-mold.

The ingot thus obtained had the following composition:

The other impurities which could be found therein (Cu, N P, As) appeared in amounts lower than 0.005%.

While we have described the preferred embodiments of our invention, it may be otherwise embodied within the scope of the appended claims.

We claim:

1. The electrolytic process for the preparation of pure manganese comprising:

(A) the preparation of an electrolytic cell having:

(i) a soluble anode bearing manganese alloy;

(ii) a cathode;

(iii) an electrolytic bath of molten salts containing at least one compound selected from the group consisting of alkaline halides and alkalineearth halides together with a manganese halide;

(B) maintaining said bath in a liquid state at about 600 C. in a confined atmoshpere;

(C) passing a direct current between said anode and said cathode such that the manganese is deposited upon said cathode;

(D) removing said cathode from the bath, dripping it in the cell, then removing it from the electrolytic cell in the open air;

(B) separating the remaining salts of the magma from the manganese.

2. The electrolytic process of claim 1 characterized by said soluble anode being formed from carburized ferromanganese.

3. The electrolytic process of claim 1 characterized by said bath of molten salts having a melting point below 530 C., said bath being maintained in a liquid state at a temperature below 530 C. in a confined atmosphere.

4. The electrolytic process of claim 3 characterized by said molten salts consisting of 20% MnCl 30% NaCl and 50% OaCl 5. The electrolytic process of claim 3 characterized by said molten salts consisting of 12% MnCl 22% NaCl, 61% CaCl and 5% KCl.

6. The electrolytic process of claim 1 characterized by passing a direct current at 0.1 to 3 volts between said anode and said cathode, with a cathodic current density of l to a./dm.

7. The electrolytic process for the preparation of pure manganese comprising:

(A) the preparation of an electrolytic cell having:

(i) a soluble anode formed of ferromanganese;

(ii) a cathode;

(iii) a bath of molten salts containing 1 to 20% MnCl 10 to 59% of at least one compound selected from the group consisting of NaCl and 5 'LiCl, 40 to 70% of at least one compound selected from the group consisting of CaCl and BaCl 0 to 10% KCl, 0 to 20% A101 (B) maintaining said bath in a liquid state at temperature below 600 C. in a confined atmosphere;

(C) passing a direct current at 0.1 to 3 volts between said anode and said cathode, with a cathodic density of from 1 to 100 a./dm. whereby the manganese is deposited upon said cathode;

(D) removing said cathode from the bath, dripping it 10 in the cell, then removing it from the electrolytic cell in the open air;

(E) separating the remaining salts of the magma from the manganese.

8. The process of claim 7 where the cathode after being removed from'the cell is placed into a furnace containing an inert gas and heated to a temperature of about 650 C. whereby the salts retained by the manganese are melted and collected.

9. The process of claim 7 where the cathode, after being removed from the cell, is placed into a furnace containing an inert atmosphere, is first heated to a temperature of about 650 C. whereby the salts retained by the manganese are melted, then is heated to a temperature higher than the melting point of manganese whereby this metal is melted under the protective layer of said molten salts.

10. The process of claim 9 where the molten manganese is cast into ingot molds under the protective layer of said molten salts.

References Cited UNITED STATES PATENTS 704,393 7/ 1902 Simon 204-64 1,861,625 6/1932 Driggs et al 20464 XR 2,398,589 4/ 1946 Mitchell 20464 3,018,233 1/1962 Welsh et al 204-64 3,028,233 4/1962 Schaefer et a1. 20464 X R FOREIGN PATENTS 602,888 8/1960 Canada.

JOHN H. MACK, Primary Examiner.

20 D. R. VALENTINE, Assistant Examiner.

U.S. Cl. XJR. 204-64, 291, 293, 294

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,450,524

June 17, 1969 Claude Pascaud et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 34, "O. 01" should read O. l line 70, "McCl should read MnCl Signed and sealed this 21st day of April 1970.

(SEAL) Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. THE ELECTROLYTIC PROCESS FOR THE PREPARATION OF PURE MANGANESE COMPRISING: (A) THE PREPARATION OF AN ELECTROLYTIC CELL HAVING: (I) A SOLUBLE ANODE BEARING MANGANESE ALLOY; (II) A CATHODE; (III) AN ELECTROLYTIC BATH OF MOLTEN SALTS CONTAINING AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALINE HALIDES AND ALKALINEEARTH HALIDES TOGETHER WITH A MANGANESE HALIDE; (B) MAINTAINING SAID BATH IN A LIQUID STATE AT ABOUT 600*C. IN A CONFINED ATMOSPHERE; (C) PASSING A DIRECT CURRENT BETWEEN SAID ANODE AND SAID CATHODE SUCH THAT THE MANGANESE IS DEPOSITED UPON, SAID CATHODE; 